To recover entrapped metal from drosses formed on melting and holding furnaces, the dross is placed in a reaction vessel and an exothermic flux is added to the dross. The dross is frequently agitated to promote coalescence of metal droplets therein. A molten metal pool forms in the bottom of the reaction vessel as the droplets coalesce. The molten metal pool is removed by draining through a bottom port. The demetallized or spent dross is then removed from the reaction vessel.
One preferred apparatus for recovering metal employing such a method is described in U.S. patent application Ser No. 09/654,314, now U.S. Pat. No. 6,464,929 for which one of the present inventors is the inventor. While the apparatus of the ""314 application can greatly facilitate recovery of metal from drosses, the apparatus has some limitations.
The apparatus of the ""314 application employs a motor to drive an impeller to agitate the dross while it is held in the reaction vessel. This apparatus, in some embodiments, has a motor which is raised and lowered by moving a motor arm to which the motor is mounted. Employing such a structure to position the motor can limit the degree of control over vertical position of the motor and the impeller, and can result in gyrations of the impeller when it encounters irregularities in the dross. These gyrations can result in damage of the impeller and/or the reaction vessel.
In some preferred embodiments, the apparatus of the ""314 application has a protective shield or hood which is mounted above the impeller. Frequently, the shield is positioned such that the impeller enters the dross before such time as the shield is in place, allowing fumes generated in the reaction vessel to escape. Furthermore, the design of the shields of the ""314application is such that they tend to a safety hazard as they are moved into position.
Another limitation is that the system of the ""314 application is designed to be operated manually, and thus depends on the skill of the operator as well the operator""s willingness to take the extra steps necessary to recover metal from the dross.
Thus, there is a need for a dross processing system which overcomes the problems discussed above.
It is an object of the invention to provide a dross reclaiming system which employs a reaction vessel covered by a hood for containment of fumes where a gravity seal is employed to maintain the hood in place on the reaction vessel.
It is another object of the invention to stabilize an impeller employed to agitate the dross against reaction forces resulting from the inhomogeneous nature of the dross.
It is a further object of the invention to provide cyclic reversing motion to the impeller to enhance separation of the metal from the dross while in the reaction vessel.
It is still a further object of the invention to provide a hood that can be swung away from the reaction vessel so as to provide an open position which enhances accessability to the reaction vessel for loading and cleaning.
It is a further object of the invention to provide a dross processing system which includes a swingable hood in combination with an impeller immobilizing mechanism to immobilize the impeller when the dross processing system is in the open position.
It is a further object of the invention to provide a dross possessing system where the position of the impeller in the reaction vessel can be varied to operate the impeller at selected depths in the dross to enhance the rate of metal separation from the dross.
It is yet another object to provide a dross processing system wherein the motions of the impeller can be programmed so as to better match the characteristics of the dross being treated.
It is another object of the invention to provide a tool for inserting a plug in a dross processing vessel when the reaction vessel is hot.
The present invention is an improved dross processing system of the type which is positionable and can be placed so as to be in close proximity with respect to a melt furnace from which the dross is to be removed. The dross processing system for which the improvement is intended has a substantially vertical support which can be positioned near the melt furnace. A reaction vessel is provided for containing the dross during the recovery process. The reaction vessel has a reaction vessel upper rim and a bottom terminating in a drain port. The reaction vessel is affixed to a reaction vessel support which in turn is pivotably mounted with respect to the substantially vertical support. Preferably, the reaction vessel is mounted to reside entirely below the reaction vessel support. The dross processing system is also provided with means for pivoting the reaction vessel between a horizontal position, where the upper rim is substantially horizontal, and a dump position, where the dross residing in the vessel is eliminated by the force of gravity.
The system to which the present improvement is applicable also has a motor mounted on a motor support arm which attaches to the substantially vertical support. The motor has a drive shaft terminating in a drive shaft free end, and can be moved between a raised motor position and one or more lowered motor positions. An impeller, having an impeller axis, attaches to the free end of the drive shaft such that, when the motor is in the raised motor position and is aligned with the reaction vessel, the impeller resides above the upper rim of the reaction vessel, and when the motor is in each of the at least one lowered motor positions and aligned with the reaction vessel, the impeller resides below the upper rim of the reaction vessel.
One aspect of the improvement of the present invention resides in providing a motor support carriage, to which the motor is mounted, and a carriage guide which attaches to the motor support arm. The carriage guide engages the motor support carriage to limit the motion of the motor so as to direct the motor along a substantially vertical path as it moves between the raised motor position and the at least one lowered motor position. The combination of the motor support carriage and the carriage guide acts to stabilize the motor, and the impeller which is mounted thereto.
Means for raising and lowering the motor support carriage relative to the motor support arm are provided, which act to move the motor and the motor support carriage between the raised motor position and each of the at least one lowered motor positions. Such means can be provided by any of the various mechanisms known in the art for raising and lowering an element of a structure. One preferred means for raising and lowering the motor support carriage is a linear actuator connected at one end to the motor support arm and at the other to the motor support carriage, which provides a means for raising and lowering the motor carriage which is simple in structure and compact. The use of the means for raising and lowering the motor support carriage relative to the motor support arm rather than moving the motor support arm to adjust the vertical position of the motor provides increased stability and positional control for the motor and the impeller.
Preferably, the carriage guide is configured not only to limit translation of the motor carriage along a substantially vertical path, but also to provide resistance to torques imparted by the action of the impeller as it agitates the dross retained in the reaction vessel. Such resistance to torques can be obtained by providing at least two stabilizing tracks, each of which slidably engages a track guide to prevent any wobbling of the motor as the impeller agitates the dross. In one preferred embodiment, the stabilizing tracks are provided by rods affixed to the motor support carriage, and the track guides are passages in the motor support arm configured to slidably engage the rods. Preferably, the stabilizing tracks and track guides are evenly spaced about the impeller axis.
While the range of motion of the motor is typically limited by the means for raising and lowering the motor support carriage and/or by the engagement between the motor support carriage and the carriage guide, in some cases it may be desirable to allow adjustably limiting the motion of the motor. Such can be achieved by employing one or more limit switches which deactivate the means for raising and lowering the motor support carriage when the motor is positioned at a desired limit of motion. The use of one or more limit switches is particularly useful to adjust the lowest lowered motor position to prevent impact of the reaction vessel by the impeller. By adjusting the position of the limit switch, the lowest lowered motor position can be altered for different configurations of impeller and/or reaction vessel.
In another aspect of the present invention, a hood is provided, having a central axis which is preferably substantially aligned with respect to the drive shaft of the motor. The hood has a downwardly extending hood rim for closing the reaction vessel to prevent escape of smoke and fumes, and a hood upper structure configured to engage the motor support carriage when the motor support carriage is moved to the raised motor position. This engagement of the hood upper structure with the motor support carriage as the motor is raised results in the hood being raised to the raised motor position along with the motor. When the motor support carriage is in the raised position, the hood rim is spaced-apart from the reaction vessel upper rim. Conversely, when the motor support carriage is moved to one of the at least one lowered motor positions, the hood rim becomes engaged with respect to the reaction vessel upper rim. In this position, the hood may directly engage the upper rim of the reaction vessel, or may engage the reaction vessel support, to which the upper rim of the reaction vessel is attached. In either case, the hood rim is brought into engagement with respect to the reaction vessel upper rim by gravity, and thus does not forcibly engage any objects which may be interposed between the hood rim and the reaction vessel upper rim, providing increased safety for the operator. Preferably, the hood upper structure is configured such that, when the motor is in one of the at least one lowered motor positions, the hood upper structure is spaced apart from the motor support carriage.
Preferably, the hood is provided with a hood port which can be opened to allow an operator to view the dross contained in the reaction vessel as it is being processed. The hood port also allows the addition of additional exothermic flux if such is needed to effectively process the dross.
Preferably, the motor support arm is configured to move between a loading/dumping position and an operating position. When the motor support arm is in the loading/dumping position, the impeller and the hood associated therewith are positioned such that their projections lie outside the footprint of the reaction vessel. When the motor support arm is in the operating position, the projection of the impeller is substantially centered with respect to the reaction vessel. Having such a loading/dumping position for the motor support arm which is displaced from the operating position facilitates loading dross into the reaction vessel for processing and dumping of the spent dross after processing, as well as reducing the required separation between the hood rim and the reaction vessel upper rim when the motor is in the raised motor position. When the motor support arm is movable, it is further preferred that both the motor and the means for raising and lowering the motor be disabled when the motor support arm is moved away from the operating position.
In a preferred embodiment, the motor support arm is rotatably mounted to the substantially vertical support to allow the motor support arm to rotate about a substantially vertical axis between the loading/dumping position and the operating position. In another aspect of the present invention, it is preferred to provide an actuating means to rotate the motor support arm between these positions, and to employ a locking means to secure the motor support arm in either position. The actuating means can be any of the various mechanisms known in the art for rotating one element with respect to another.
Preferably, the motor is operated to move the impeller in a cyclic reversing motion where the impeller is rotated in one direction for a time period, then reversed and rotated in the opposite direction for a time period, with this action being repeated for the desired processing duration. It is further preferred for the motor to have an overload sensor to reverse the direction of the motor when the impeller encounters resistance above a predetermined set point. When the motor is a hydraulic motor, such an overload sensor can be provided by a sensor which monitors the pressure in the hydraulic circuit that drives the motor and reverses the motor when the pressure increases to a predetermined level.
When it is desired to automate the operation of the dross processing system, the dross processing system can be provided with a control system for selectively and sequentially activating various elements of the system to allow the processing of the dross with minimal operator interaction. Although the control system can be built with dedicated circuits, it is preferred to employ a microprocessor with appropriate instruction sets to facilitate the automation of the operation, since its programming allows great flexibility to allow a broad range of cycles to be handled by a single control system.
The degree of control provided when a microprocessor is employed depends on the automation sought. In an elementary form, the microprocessor can be employed to control the dross processing cycle by controlling the entry of the impeller into the dross, the length of the cycle, the character of the cycle (e.g., interval motor runs in one direction before reversing, depth profile over time of the impeller, etc.), and the removal of the impeller from the dross. The parameters of the cycle depend, in part, on the characteristics of the dross. The ability to program the action of the motor allows repeating a desired cycle which has been found by experience to be effective for dross having a particular character. In a more automated system, the microprocessor can also control other aspects of the system, such as the means for pivoting the reaction vessel between a horizontal position and a dump position.
The improved dross processing system of the present invention can employ various types of impellers for stirring the reacting dross. In one preferred impeller configuration, the impeller is provided with a first agitator surface having at least one pair of first agitator blades which are opposed. When such a configuration is employed, it is further preferred that a second agitator surface be provided and that the first agitator surface have blades with opposing pitches with respect to the blades of the second agitator surface. When the reaction vessel has a sloped bottom, it is preferred for the angle of the agitator blades to match the draft angle of the bottom of the reaction vessel.
To facilitate the accurate placement of a plug to seal the drain port of the reaction vessel, a plug setting tool can be provided. The plug setting tool has a tube sized to frictionally accept the plug, and a plunger which can be depressed to eject the plug from the tube. Preferably, the tube has an end region sized to be insertable into the drain port to align the tube with the drain port before the plug is ejected from the tube into the drain port.